I am using two operating systems. First I installed Win98 on C: drive and then I installed WinXp on D: Drive.
My question is that I had to reinstall the Win98 after formating my C: drive, then with new installation, there is no option to select to OS, so I am not able to run WinXp. Whenever I boot the system, it starts win98.

Where is that OS selection option?
Is there any way to bring it back?
How can I prevent it to happen again?